The organic electroluminescent (EL) is a luminous phenomenon in which the organic materials convert the electrical energy directly into light energy under an electric field. In early stage, due to such reasons as high voltage of the driver system, low luminous efficiency of the device, the research on organic electroluminescent was stagnated. In 1987, Tan et al (Kodak Corporation) invented 8-hydroxyquinoline aluminum (Alq3) as light-emitting materials, which can be made into a uniform, dense, high-quality thin film with aromatic diamine, such that the organic electroluminescent device was prepared with significantly increasing brightness and luminescent efficiency under low working voltage, and a research on new prologue electroluminescent materials was opened. However, due to the restriction of the spin statistics theory, the internal quantum efficiency of the fluorescent material was merely 25% in theory, thus it became a hot research directions in the field thereafter that how to make full use of the remaining 75% of the phosphorescence to achieve higher luminous efficiency. In 1997, Forrest et al discovered phosphorus electroluminescent phenomenon, and the internal quantum efficiency of the subsequently obtained organic electroluminescent material broke through the 25% limit, thus leading the research of the organic electroluminescent material into another new period.
In nowadays study of organic electroluminescent material, complexes of transition metal, such as complexes of iridium, ruthenium, platinum, etc., doped with small molecule have become a research focus. The advantages of the complexes are that they can obtain a high energy emitted from the triplet of their own, and the metal iridium (III) compounds, because of the good stability, mild reaction conditions in the synthesis process, and the high electroluminescent properties, have occupied the dominant position in the subsequent study. Nevertheless, conventional iridium containing organic electroluminescent material, such as bis[2-(2,4-difluorophenyl-yl)pyridine-N, C2](pyridine-formic acid) combined iridium (FIrpic), bis[2-(2,4-difluoro-3-cyanophenyl)pyridine-N, C2] (four pyrazole boron) iridium (Fir6) and the like, have a poor internal quantum efficiency and electroluminescent efficiency, thus limiting the development of the research on organic electroluminescent technology.